The invention relates to an arrangement for measuring the viscosity of a fluid.
More particularly, the invention relates to an arrangement for measuring the viscosity of a fluid by determining the time required for a standard element to travel a predetermined distance through the fluid.
Viscosity measurements are performed with either a discharge or falling ball viscometer. In the discharge viscometer, the time required for a predetermined quantity of the fluid to flow through an opening of predetermined cross section is measured. In the falling ball viscometer, on the other hand, the time required for a standard element, e.g. a sphere, of known weight and dimensions to fall a predetermined distance through a column of the fluid is measured. The viscosity in each case is a function of the elapsed time which is normally measured with a stop watch.
It has been found that precise time measurements cannot be obtained with conventional viscometers. Accordingly, the viscosity cannot be determined with the desired accuracy. This is especially true for viscometers which are intended to be transportable.
The falling ball viscometer is particularly prone to inaccuracies. These inaccuracies stem from parallax. Thus, the falling ball viscometer has a transparent vessel which accommodates the fluid and is engraved with marks which respectively indicate the beginning and end of the zone along which the standard element is timed. Parallax makes it difficult to determine the precise instant at which the standard element passes a mark. The errors due to parallax are particularly large in the frequent cases where viscosity measurements are performed on murky fluids such as, for example, used motor oil, lubricating oil and fuel. Here, the murkiness of the fluid affects the precision of the timing to such a degree that a well-defined viscosity cannot be obtained and the viscosity can be determined only to within a predetermined scatter range.
Furthermore, the known viscometers are primarily designed for use at a fixed location and are difficult to transport. However, there are situations where it is desirable to have a truly portable viscometer. For instance, it is highly desirable to rapidly measure the viscosity of fuel oil at the point of delivery.
Moreover, the determination of viscosity with conventional viscometers is inconvenient in that it requires the use of tables which relate the viscosity to the time required for the standard element to travel a predetermined distance through the fluid. Aside from the inconvenience, significant errors in addition to those arising from parallax may occur from inaccuracies in the tables.